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Synthesis, processing and export of cytoplasmic endo‐β‐1,4‐xylanase from barley aleurone during germination
Author(s) -
Caspers Martien P. M.,
Lok Finn,
Sinjorgo Karin M. C.,
Van Zeijl Mieke J.,
Nielsen Kirsten A.,
CameronMills Verena
Publication year - 2001
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.0960-7412.2001.01019.x
Subject(s) - aleurone , xylanase , cytoplasm , secretion , biochemistry , extracellular , germination , enzyme , biology , microbiology and biotechnology , botany
Summary We have identified the major endo‐β‐1,4‐xylanase (XYN‐1) in the aleurone of germinating barley grain, and show that it is expressed as a precursor of M r 61 500 with both N‐ and C‐terminal propeptides. XYN‐1 is synthesized as an inactive enzyme in the cytoplasm, and only becomes active at a late stage of germination when the aleurone ceases to secrete hydrolases. A series of processing steps, mediated in part by aleurone cysteine endoproteases, yields a mature active enzyme of M r 34 000. Processing and extracellular release of the mature enzyme coincide with the programmed cell death (PCD)‐regulated disintegration of aleurone cells. We discuss the significance of delayed aleurone cell‐wall degradation by endoxylanases in relation to the secretory capacity of the aleurone, and propose a novel role for aleurone PCD in facilitating the export of hydrolases.